Mechanics Instead of Microchip Fully Mechanical 8-Bit Computer Made from Toy Elements

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Wuxi InfiMotion Technology Co., Ltd.

The latest creation by a YouTube tinkerer computes with gears, levers, and shafts, entirely mechanically and without electricity. The self-built mechanical 8-bit computer already performs additions, subtractions, and initial logical operations.

A computer that clicks instead of beeps: what sounds like steampunk is the latest project by "Shadowman," who regularly showcases mechanical constructions on YouTube. His goal: a fully mechanical computer capable of processing 8-bit binary numbers—meaning values between 0 and 255, or -128 to 127 in two's complement. Its core components are a simple arithmetic logic unit (ALU), several registers for intermediate storage, and a sophisticated gear system for data processing.

Gears Calculate in Binary

"The ALU is the heart of the computer," says Shadowman in his latest video. There, he explains in detail how two binary numbers are added using mechanical components. The inputs are made via two registers, whose bits are encoded by movable pins. Depending on their position, pushed in or pulled out, the system counts the respective bits as zero or one. The calculation logic works similarly to school arithmetic: the sum of a pair of bits creates a new bit, and in the case of a carry, the value is passed to the next position.

Rotational movements are transmitted via a chain with cams to eight parallel crankshafts. These drive the corresponding gears for each calculation step. "The pins on the chain act like a mechanical clock," explains the inventor. Exact positioning is secured by weights that prevent snapping back. A safety mechanism with a spring decouples the drive system under excessive load—although, as Shadowman admits, it is not yet entirely reliable.

Bitwise Logic With Lever Switching

In addition to addition and subtraction, the ALU can also perform simple logical operations: AND, XOR, bit inversion, or decrementation. The specific function is set via mechanical levers. "To subtract, I invert the B register and add one—just as you do with two's complement," explains Shadowman. This, too, works through movable elements that mirror all bits when rotated 90 degrees.

For the logical operations, the starting positions of the counting mechanisms are manipulated. In AND mode, for example, the counter starts one position earlier, so an output bit is only produced when both input bits are one. XOR, on the other hand, uses a targeted reversal of the shaft movement to bypass carry mechanisms. "The whole thing is almost like a mechanical puzzle," says Shadowman.

Three Simple Flags for Later Program Control

Important for future programs are the state flags: a zero flag, a negative flag, and an overflow flag. These are derived through simple physical effects: a movable bar detects if all sum bits are zero, the most significant bit indicates a negative number when set to one, and an additional carry pin signals an overflow of the value.

Much is still unfinished. Register sets for RAM and ROM are on the agenda, as is data transfer between the modules. Nevertheless, the project impressively demonstrates that digital logic, as in the past, is also possible entirely without microelectronics—solely with levers, rods, and a clever system of gears. (mc)

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